U.S. patent application number 11/340591 was filed with the patent office on 2006-08-24 for honeycomb structured body.
Invention is credited to Atsushi Kudo, Kazushige Ohno.
Application Number | 20060188415 11/340591 |
Document ID | / |
Family ID | 34467781 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060188415 |
Kind Code |
A1 |
Ohno; Kazushige ; et
al. |
August 24, 2006 |
Honeycomb structured body
Abstract
A honeycomb structured body of the present invention is a
pillar-shaped honeycomb structured body comprising a large number
of through holes that are longitudinally placed in parallel with
one another with a partition wall therebetween, wherein the large
number of through holes include a group of large-capacity through
holes being sealed at one of end portions so that the sum of areas
on a cross section perpendicular to the longitudinal direction is
made relatively larger, and a group of small-capacity through holes
being sealed at the other end portion so that the sum of areas on
the cross section is made relatively smaller, and the partition
wall that separates the adjacent through holes constituting the
group of large-capacity through holes is provided with a selective
catalyst supporting portion used for selectively supporting a
catalyst.
Inventors: |
Ohno; Kazushige; (Gifu,
JP) ; Kudo; Atsushi; (Gifu, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
34467781 |
Appl. No.: |
11/340591 |
Filed: |
January 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP04/15507 |
Oct 20, 2004 |
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11340591 |
Jan 27, 2006 |
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Current U.S.
Class: |
422/177 |
Current CPC
Class: |
B01D 46/0063 20130101;
F01N 3/0222 20130101; B01D 46/2474 20130101; B01D 46/2451 20130101;
C04B 2111/0081 20130101; B01D 2046/2485 20130101; B01D 2046/2481
20130101; F01N 2240/20 20130101; B01D 46/247 20130101; C04B 38/0012
20130101; Y10T 428/24165 20150115; F01N 2330/48 20130101; Y02T
10/12 20130101; B01J 35/04 20130101; Y10T 428/24157 20150115; Y10T
428/24149 20150115; F01N 2330/06 20130101; B01D 46/2459 20130101;
B01D 2046/2496 20130101; F01N 2330/34 20130101; F01N 2260/06
20130101; B01D 46/2455 20130101; B01D 46/2466 20130101; B01D 53/94
20130101; C04B 38/0012 20130101; C04B 35/00 20130101 |
Class at
Publication: |
422/177 |
International
Class: |
B01D 53/34 20060101
B01D053/34 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2003 |
JP |
2003-359235 |
Oct 22, 2003 |
JP |
2003-362512 |
Claims
1. A pillar-shaped honeycomb structured body comprising a large
number of through holes that are longitudinally placed in parallel
with one another with a partition wall therebetween, wherein said
large number of through holes include a group of large-capacity
through holes being sealed at one of end portions so that the sum
of areas on a cross section perpendicular to the longitudinal
direction is made relatively larger, and a group of small-capacity
through holes being sealed at the other end portion so that the sum
of areas on said cross section is made relatively smaller, and said
partition wall that separates the adjacent through holes
constituting said group of large-capacity through holes is provided
with a selective catalyst supporting portion used for selectively
supporting a catalyst.
2. The honeycomb structured body according to claim 1, wherein a
catalyst is supported at least on the selective catalyst supporting
portion.
3. The honeycomb structured body according to claim 1, wherein said
catalyst comprises at least one kind selected from the group
consisting of a noble metal, an alkali metal, an alkaline earth
metal, a rare-earth element, and a transition metal element.
4. The honeycomb structured body according to claim 3, wherein said
noble metal comprises at least one kind selected from the group
consisting of platinum, palladium, and rhodium.
5. The honeycomb structured body according to claim 1, wherein the
selective catalyst supporting portion is a protruded portion and/or
a recessed portion formed on the partition wall that separates
adjacent through holes constituting the group of large-capacity
through holes.
6. The honeycomb structured body according to claim 5, wherein the
protruded portion formed on the partition wall that separates
adjacent through holes constituting the group of large-capacity
through holes has a shape widened toward the base.
7. The honeycomb structured body according to claim 5, wherein a
number of protruded portions are formed on each of said partition
walls so as to prepare a corrugated surface on each of said
partition walls.
8. The honeycomb structured body according to claim 5, wherein the
shape of the recessed portion formed on said partition wall that
separates adjacent through holes constituting the group of
large-capacity through holes is a concave shape or a grooved
shape.
9. The honeycomb structured body according to claim 5, wherein said
protruded portion and/or recessed portion formed on the partition
wall that separates adjacent through holes constituting the group
of large-capacity through holes are continuously formed from the
end on the inlet side of said through hole to the end on the outlet
side of said through hole.
10. The honeycomb structured body according to claim 5, wherein the
protruded portion formed at the selective catalyst supporting
portion has a height of at least about 0.02 time and at most about
6 times the thickness of the partition wall that separates adjacent
through holes constituting the group of large-capacity through
holes.
11. The honeycomb structured body according to claim 5, wherein the
recessed portion formed at the selective catalyst supporting
portion has a depth of at least about 0.02 time and at most about
0.4 time the thickness of the partition wall that separates
adjacent through holes constituting the group of large-capacity
through holes.
12. The honeycomb structured body according to claim 1, wherein a
thickness of a partition wall that separates adjacent through holes
constituting the group of large-capacity through holes is at least
about 0.2 mm and at most about 1.2 mm.
13. The honeycomb structured body according to claim 1, wherein a
thickness of a partition wall that separates adjacent through holes
constituting the group of large-capacity through holes is formed to
be thicker than a thickness of a partition wall that separates
adjacent through holes constituting the group of large-capacity
through holes and through holes constituting the group of
small-capacity through holes.
14. The honeycomb structured body according to claim 1, wherein the
through holes that constitute the group of large-capacity through
holes and/or the through holes that constitute the group of
small-capacity through holes have a cross-sectional shape
perpendicular to the longitudinal direction thereof which is a
polygonal shape.
15. The honeycomb structured body according to claim 1, wherein the
cross-sectional shape perpendicular to the longitudinal direction
of the through holes that constitute the group of large-capacity
through holes is an octagonal shape, and the cross-sectional shape
perpendicular to the longitudinal direction of the through holes
that constitute the group of small-capacity through holes is a
quadrangular shape.
16. The honeycomb structured body according to claim 1, wherein a
ratio of the sum of areas on a cross section perpendicular to the
longitudinal direction of the through holes that constitute the
group of large-capacity through holes to the sum of areas on the
cross section perpendicular to the longitudinal direction of the
through holes that constitute the group of small-capacity through
holes is at least about 1.5 and at most about 2.7.
17. The honeycomb structured body according to claim 1, wherein
said honeycomb structured body is mainly made from a porous ceramic
material.
18. The honeycomb structured body according to claim 17, wherein
said honeycomb structured body comprises at least one kind selected
from the group consisting of nitride ceramics, carbide ceramics, or
oxide ceramics.
19. The honeycomb structured body according to claim 17, wherein a
porosity of said honeycomb structured body is at least about 20%
and at most about 80%.
20. The honeycomb structured body according to claim 17, wherein an
average pore diameter of said honeycomb structured body is at least
about 1 .mu.m and at most about 100 .mu.m.
21. The honeycomb structured body according to claim 1, wherein, on
the cross section perpendicular to the longitudinal direction, at
least one of angles formed by crossing of the partition wall that
separates adjacent through holes constituting the group of
large-capacity through holes and the partition wall that separates
adjacent through holes, one of which constituting the group of
large-capacity through holes and the other of which constituting
the group of small-capacity through holes, is an obtuse angle.
22. The honeycomb structured body according to claim 1, wherein, on
the cross section perpendicular to the longitudinal direction, the
vicinity of each of corners of the through hole constituting the
group of the large-capacity through holes and/or the through hole
constituting the group of the small-capacity through holes is
formed by a curved line.
23. The honeycomb structured body according to claim 1, wherein the
distance between centers of gravity on a cross section
perpendicular to the longitudinal direction of adjacent through
holes constituting the group of the large-capacity through holes is
equal to the distance between centers of gravity on a cross section
perpendicular to the longitudinal direction of adjacent through
holes constituting the group of the small-capacity through
holes.
24. The honeycomb structured body according to any one of claims 1
to 23, which is used for an exhaust gas purifying device in a
vehicle.
25. A honeycomb structured body comprising: a honeycomb block
formed by combining a plurality of the honeycomb structured bodies
according to any one of claims 1 to 23 together through a sealing
material layer; and a sealing material layer which is formed on the
peripheral face of said honeycomb block, wherein the sealing
material layer is made from a material that hardly lets gases pass
through in comparison with said honeycomb structured body.
26. The honeycomb structured body according to claim 25, which is
used for an exhaust gas purifying device in a vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims benefit of priority based on JP-A
2003-359235 filed on Oct. 20, 2003, JP-A 2003-362512 filed on Oct.
22, 2003 and PCT/JP2004/015507 filed on Oct. 20, 2004. The contents
of these applications are incorporated herein by reference in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a honeycomb structured body
used as a filter for removing particulates and the like contained
in exhaust gases, a catalyst supporting member, and the like.
[0004] 2. Discussion of the Background
[0005] In recent years, particulates such as soot and the like
contained in exhaust gases discharged from internal combustion
engines of vehicles, such as buses and trucks, and construction
machines, have raised serious problems as those particulates are
harmful to the environment and the human body.
[0006] There have been proposed various honeycomb structured bodies
made from porous ceramics, which serve as filters capable of
collecting particulates in exhaust gases to convert the exhaust
gases.
[0007] Conventionally, with respect to the honeycomb structured
body of this type, a filter having the following structure has been
proposed: two kinds of through holes, that is, a group of through
holes with a relatively large capacity (hereinafter, referred to as
large-capacity through hole) and a group of through holes with a
relatively small capacity (hereinafter, referred to as
small-capacity through hole), are prepared, and each of the
large-capacity through holes is sealed with a plug at one of ends,
and each of the small-capacity through holes is sealed with a plug
at the other opposite end. Moreover, the honeycomb structured body
that is designed to have another structure in which the
large-capacity through hole has an opening on a gas inlet side of a
filter while the small-capacity through hole has an opening on a
gas outlet side of the filter has been proposed (for example, see
JP-A56-124418, JP-A62-96717, JUM-A58-92409, U.S. Pat. No.
4,416,676, JP-A 58-196820, U.S. Pat. No. 4,420,316, JP-A 58-150015,
JP-A 5-68828, French Patent No. 2789327, International Publication
No. WO02/100514, International Publication No. WO02/10562, and
International Publication No. WO03/20407).
[0008] There have been also known filters and the like having a
structure in which the number of through holes that have openings
on the gas inlet side (hereinafter, referred to as inlet-side
through holes) is made greater than the number of through holes
that have openings on the gas outlet side (hereinafter, referred to
as outlet-side through holes) so that the total amount of surface
areas on the inlet-side through holes is made relatively greater
than the total amount of surface areas on the outlet-side through
holes (for example, see FIG. 3 of JP-A 58-196820).
[0009] When viewed from the end face, these honeycomb structured
bodies are constituted by two types of through holes, that is, a
group of large-capacity through holes (the total amount of rates of
surface area/cross-sectional area of the through holes is
relatively large) and a group of small-capacity through holes (the
total amount of rates of surface area/cross-sectional area of the
through holes is relatively small).
[0010] The contents of JP-A 56-124418, JP-A 62-96717, J UM-A
58-92409, U.S. Pat. No. 4,416,676, JP-A 58-196820, U.S. Pat. No.
4,420,316, JP-A58-150015, JP-A5-68828, French Patent No. 2789327,
International Publication No. WO02/100514, International
Publication No. WO02/10562, and International Publication No.
WO03/20407 are incorporated herein by reference in their
entirety.
SUMMARY OF THE INVENTION
[0011] In accordance with a first aspect of the present invention,
provided is
[0012] a pillar-shaped honeycomb structured body comprising a large
number of through holes that are longitudinally placed in parallel
with one another with a partition wall therebetween,
[0013] wherein
[0014] the large number of through holes include a group of
large-capacity through holes being sealed at one of the end
portions so that the sum of areas on a cross section perpendicular
to the longitudinal direction is made relatively larger, and a
group of small-capacity through holes being sealed at the other end
portion so that the sum of areas on the cross section is made
relatively smaller, and
[0015] the partition wall that separates the adjacent through holes
constituting the group of large-capacity through holes is provided
with a selective catalyst supporting portion used for selectively
supporting a catalyst.
[0016] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, a catalyst is
supported at least on the selective catalyst supporting portion,
and the catalyst comprises at least one kind selected from the
group consisting of a noble metal, an alkali metal, an alkaline
earth metal, a rare-earth element, and a transition metal element.
Furthermore, it is desirable that the noble metal comprises at
least one kind selected from the group consisting of platinum,
palladium, and rhodium.
[0017] Moreover, desirably, the selective catalyst supporting
portion is a protruded portion and/or a recessed portion formed on
the partition wall that separates adjacent through holes
constituting the group of large-capacity through holes. The
protruded portion formed on the partition wall that separates
adjacent through holes constituting the group of large-capacity
through holes desirably has a shape widened toward the base, while
a number of protruded portions are desirably formed on each of the
partition walls so as to prepare a corrugated surface on each of
the partition walls. On the other hand, the shape of the recessed
portion formed on the partition wall that separates adjacent
through holes constituting the group of large-capacity through
holes is desirably a concave shape or a grooved shape, while it is
desirable that the protruded portion and/or recessed portion formed
on the partition wall that separates adjacent through holes
constituting the group of large-capacity through holes are
continuously formed from the end on the inlet side of the through
hole to the end on the outlet side of the through hole.
[0018] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, the protruded
portion formed at the selective catalyst supporting portion has a
height of at least about 0.02 time and at most about 6 times the
thickness of the partition wall that separates adjacent through
holes constituting the group of large-capacity through holes, and
the recessed portion formed at the selective catalyst supporting
portion has a depth of at least about 0.02 time and at most about
0.4 time the thickness of the partition wall that separates
adjacent through holes constituting the group of large-capacity
through holes.
[0019] Furthermore, it is desirable that a thickness of a partition
wall that separates adjacent through holes constituting the group
of large-capacity through holes is at least about 0.2 mm and at
most about 1.2 mm. It is also desirable that a thickness of a
partition wall that separates adjacent through holes constituting
the group of large-capacity through holes is formed to be thicker
than a thickness of a partition wall that separates adjacent
through holes constituting the group of large-capacity through
holes and through holes constituting the group of small-capacity
through holes.
[0020] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, the through holes
that constitute the group of large-capacity through holes and/or
the through holes that constitute the group of small-capacity
through holes have a cross-sectional shape perpendicular to the
longitudinal direction thereof which is a polygonal shape.
[0021] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, the
cross-sectional shape perpendicular to the longitudinal direction
of the through holes that constitute the group of large-capacity
through holes is an octagonal shape, and the cross-sectional shape
perpendicular to the longitudinal direction of the through holes
that constitute the group of small-capacity through holes is a
quadrangular shape.
[0022] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, a ratio of the
sum of areas on a cross section perpendicular to the longitudinal
direction of the through holes that constitute the group of
large-capacity through holes to the sum of areas on the cross
section perpendicular to the longitudinal direction of the through
holes that constitute the group of small-capacity through holes is
at least about 1.5 and at most about 2.7.
[0023] It is desirable that the honeycomb structured body in
accordance with the first aspect of the present invention is mainly
made from a porous ceramic material, and that the honeycomb
structured body comprises at least one kind selected from the group
consisting of nitride ceramics, carbide ceramics, or oxide
ceramics. Moreover, desirably, a porosity of the honeycomb
structured body is at least about 20% and at most about 80%, while
an average pore diameter of the honeycomb structured body is at
least about 1 .mu.m and at most about 100 .mu.m.
[0024] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably,
[0025] on the cross section perpendicular to the longitudinal
direction,
[0026] at least one of angles formed by crossing of
[0027] the partition wall that separates adjacent through holes
constituting the group of large-capacity through holes and
[0028] the partition wall that separates adjacent through holes,
one of which constituting the group of large-capacity through holes
and the other of which constituting the group of small-capacity
through holes,
[0029] is an obtuse angle.
[0030] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, on the cross
section perpendicular to the longitudinal direction, the vicinity
of each of corners of the through hole constituting the group of
the large-capacity through holes and/or the through hole
constituting the group of the small-capacity through holes is
formed by a curved line.
[0031] In the honeycomb structured body in accordance with the
first aspect of the present invention, desirably, the distance
between centers of gravity on a cross section perpendicular to the
longitudinal direction of adjacent through holes constituting the
group of the large-capacity through holes is equal to the distance
between centers of gravity on across section perpendicular to the
longitudinal direction of adjacent through holes constituting the
group of the small-capacity through holes.
[0032] In accordance with a second aspect of the present invention,
provided is a honeycomb structured body comprising: a honeycomb
block formed by combining a plurality of the honeycomb structured
bodies according to the first aspect of the present invention
together through a sealing material layer; and a sealing material
layer which is formed on the peripheral face of the honeycomb
block, wherein the sealing material layer is made from a material
that hardly lets gases pass through in comparison with the
honeycomb structured body.
[0033] In addition to the case where the honeycomb structured
bodies of the first aspect of the present invention are used as
constituent members for the honeycomb structured body in accordance
with the second aspect of the present invention, only a single
honeycomb structured body of the first aspect of the present
invention may be used for a filter.
[0034] In the following description, a honeycomb structured body
having a structure as one integral unit as a whole, that is, the
honeycomb structured body in accordance with the first aspect of
the present invention, is also referred to as an integral honeycomb
structured body, and a honeycomb structured body having a structure
in which a plurality of ceramic members are combined together
through a sealing material layer, that is, the honeycomb structured
body in accordance with the second aspect of the present invention,
is also referred to as an aggregated honeycomb structured body.
Here, in the case where no discrimination is required between the
integral honeycomb structured body and the aggregated honeycomb
structured body, the corresponding structured body is referred to
as a honeycomb structured body.
[0035] The honeycomb structured body according to the first or
second aspect or the present invention is desirably used for an
exhaust gas purifying (converting) device in a vehicle.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1A is a perspective view that schematically shows one
example of an integral honeycomb structured body of the present
invention, FIG. 1B is a cross-sectional view taken along line A-A
of the integral honeycomb structured body of the present invention
shown in FIG. 1A, and FIG. 1C is a front view that schematically
shows another example of the integral honeycomb structured body of
the present invention.
[0037] FIG. 2 is a cross-sectional view that schematically shows a
cross section perpendicular to the longitudinal direction of a
honeycomb structured body of the present invention in which the
number of large-capacity through holes 101 and the number of
small-capacity through holes 102 are approximately set to 1:2.
[0038] FIGS. 3A to 3D are cross-sectional views each of which
schematically shows a cross section perpendicular to the
longitudinal direction of an integral honeycomb structured body of
the present invention, and FIG. 3E is a cross-sectional view that
schematically shows a cross section perpendicular to the
longitudinal direction of a conventional integral honeycomb
structured body.
[0039] FIGS. 4A to 4F are cross-sectional views each of which
schematically shows one portion of a cross section perpendicular to
the longitudinal direction of an integral honeycomb structured body
of the present invention.
[0040] FIG. 5 is a cross-sectional view that schematically shows
one example of a cross section perpendicular to the longitudinal
direction of an integral honeycomb structured body of the present
invention.
[0041] FIG. 6 is a perspective view that schematically shows one
example of an aggregated honeycomb structured body of the present
invention.
[0042] FIG. 7 is a cross-sectional view that schematically shows
one example of an exhaust gas purifying (converting) device for a
vehicle in which the honeycomb structured body of the present
invention is placed.
[0043] FIG. 8 is a cross-sectional view that schematically shows
one example of a conventional honeycomb structured body.
DESCRIPTION OF THE EMBODIMENTS
[0044] In the integral honeycomb structured body of the present
invention, provided is
[0045] a pillar-shaped honeycomb structured body comprising a large
number of through holes that are longitudinally placed in parallel
with one another with a partition wall therebetween,
[0046] wherein
[0047] the large number of through holes include a group of
large-capacity through holes being sealed at one of the end
portions so that the sum of areas on a cross section perpendicular
to the longitudinal direction is made relatively larger, and a
group of small-capacity through holes being sealed at the other end
portion so that the sum of areas on the cross section is made
relatively smaller, and
[0048] the partition wall that separates the adjacent through holes
constituting the group of large-capacity through holes is provided
with a selective catalyst supporting portion used for selectively
supporting a catalyst.
[0049] With respect to combinations between the group of
large-capacity through holes and the group of small-capacity
through holes, the following combinations are proposed: (1)
individual through hole constituting the group of large-capacity
through holes and individual through hole constituting the group of
small-capacity through holes have the equal area of the cross
section perpendicular to the longitudinal direction, with the
number of the through holes constituting the group of
large-capacity through holes being greater; (2) individual through
hole constituting the group of large-capacity through holes and
individual through hole constituting the group of small-capacity
through holes are different from each other in the area of the
cross section perpendicular to the longitudinal direction, with the
numbers of the through holes of the two types being different from
each other; and (3) individual through hole constituting the group
of large-capacity through holes has a larger area of the cross
section compared to individual through hole constituting the group
of small-capacity through holes, with the numbers of the though
holes of the two types being the same.
[0050] Moreover, with respect to the through holes constituting the
group of large-capacity through holes and/or the through holes
constituting the group of small-capacity through holes, through
holes of one type having the same shape and the same area in the
cross section perpendicular to the longitudinal direction may be
used, or through holes of two or more types having different shapes
and different areas in the cross section perpendicular to the
longitudinal direction may be used.
[0051] In the honeycomb structured body of the present invention,
the shape serving as a basic unit is repeated, and in view of the
basic unit, the ratios of areas of the cross section are different
from each other. In this case, however, in portions closer to the
periphery, there is a basic unit with a portion chipped and this
part is not conformed to the above-mentioned rule. Therefore, when
measurements are strictly carried out up to one or two cells on the
periphery, the calculations need to be carried out by excluding the
one or two cells, or the calculations need to be carried out
excluding portions that are not repetitions of the basic units.
More specifically, for example, as shown in FIG. 8, a honeycomb
structured body having a structure in which: the shapes of a cross
section perpendicular to the longitudinal direction of the through
holes are the same except for those in the vicinity of the
periphery; one of ends of the through holes having the same
cross-sectional shape is sealed: and sealed portions and opened
portions of each of the ends are placed in a manner so as to form a
checked pattern as a whole, is not included in the honeycomb
structured body of the present invention.
[0052] FIG. 1A is a perspective view that schematically shows one
example of an integral honeycomb structured body of the present
invention, FIG. 1B is a cross-sectional view taken along line A-A
of the integral honeycomb structured body of the present invention
shown in FIG. 1A, and FIG. 1C is a front view that schematically
shows another example of the integral honeycomb structured body of
the present invention.
[0053] In view of the combinations of the group of large-capacity
through holes and the group of small-capacity through holes,
integral honeycomb structured bodies 20 and 30, shown in FIGS. 1A
to 1C, correspond to the above-mentioned combination (3). In other
words, in comparison with the individual through hole constituting
the large-capacity through holes and the individual through hole
constituting the small-capacity through holes, the area of the
cross section of the through hole constituting the group of the
large-capacity through holes is larger, with the numbers of the
though holes of the two types being the same.
[0054] In the following, the through holes constituting the
large-capacity through holes are also simply referred to as
large-capacity through holes, and the through holes constituting
the small-capacity through holes are also simply referred to as
small-capacity through holes.
[0055] As shown in FIGS. 1A and 1B, the integral honeycomb
structured body 20 having an approximately square pillar shape
comprises a number of through holes 21 longitudinally placed in
parallel together with a partition wall 23 interposed therebetween.
The through holes 21 include two kinds of through holes, that is,
large-capacity through holes 21a with ends on the gas outlet side
of the integral honeycomb structured body 20 sealed with plugs 22
and small-capacity through holes 21b with ends on the gas inlet
side of the integral honeycomb structured body 20 sealed with plugs
22, and the area on the cross section perpendicular to the
longitudinal direction of the large-capacity through holes 21a is
made relatively greater in comparison with that of the
small-capacity through holes 21b. The partition wall 23 that
separates these through holes 21 from each other is allowed to
serve as a filter. In other words, exhaust gases that have entered
the large-capacity through holes 21a are allowed to flow out of the
small-capacity through holes 21b after always passing through the
partition wall 23.
[0056] In this integral honeycomb structured body 20, a selective
catalyst supporting portion, prepared as a protruded portion 24, is
formed on the partition wall 23b that separates adjacent
large-capacity through holes 21a from each other.
[0057] Moreover, as shown in FIG. 1C, an integral honeycomb
structured body 30 according to another embodiment comprises a
number of through holes 31 longitudinally placed in parallel
together with a partition wall 33 interposed therebetween, and the
through holes 31 include two kinds of through holes, that is,
large-capacity through holes 31a with ends on the gas outlet side
sealed with plugs 32 and small-capacity through holes 31b with ends
on the gas inlet side sealed with plugs 32. The area on the cross
section perpendicular to the longitudinal direction of the
large-capacity through holes 31a is made relatively larger in
comparison with that of the small-capacity through holes 31b. The
partition wall 33 that separates these through holes 31 from each
other is allowed to serve as a filter. In other words, exhaust
gases that have entered the large-capacity through holes 31a are
allowed to flow out of the small-capacity through holes 31b after
always passing through the partition wall 33.
[0058] In this integral honeycomb structured body 30, a selective
catalyst supporting portion, prepared as a recessed portion 34, is
formed on the partition wall 33b that separates adjacent
large-capacity through holes 31a from each other.
[0059] As described above, in the integral honeycomb structured
body 20, 30 of the present invention, a selective catalyst
supporting portion used for selectively supporting a catalyst is
formed on the partition wall that separates adjacent large-capacity
through holes 21a, 31a. The selective catalyst supporting portion
is not particularly limited as long as it is formed on the
partition wall 23b, 33b that separates adjacent large-capacity
through holes 21a, 31a from each other so as to selectively (in a
concentrating manner) support a catalyst. For example, a protruded
portion 24 as shown in FIG. 1A or a recessed portion 34 as shown in
FIG. 1C may be used, or a roughened surface or the like, in which
the surface roughness of the partition wall 23b, 33b is increased,
may also be used.
[0060] In the structure in which the protruded portion 24 is formed
on the partition wall 23b, when the base member of a honeycomb
structured body is impregnated with a solution containing a
catalyst or a catalyst material and then taken out, the droplets of
the solution are retained on the periphery of the protruded portion
24 by the use of surface tension of the solution; thereafter, by
heating and drying the resulting base member, a large amount of
catalyst can be supported on the protruded portion 24 and the
vicinity thereof. Moreover, when the protruded portion 24 is formed
on the partition wall 23b, it is possible to improve the thermal
conductivity and also to increase the regenerating rate.
[0061] With respect to the shape of the protruded portion 24 to be
formed on the partition wall 23b that separates adjacent
large-capacity through holes 21a from each other, although not
particularly limited, a shape which easily maintains droplets and
ensures a certain degree of strength is desirable and, more
specifically, a shape widened toward the base is desirable. The
protruded portion having the widened shape toward the base easily
provides higher strength in comparison with a protruded portion
that is thinly elongated. Moreover, the protruded portion is
desirably formed continuously from the end on the inlet side of the
integral honeycomb structured body 20 to the end on the outlet side
thereof. This structure provides high strength and allows a forming
process through extrusion molding.
[0062] With respect to the height of the protruded portion 24,
although not particularly limited, a desirable lower limit thereof
is about 0.02 time the thickness of the partition wall 23b that
separates adjacent large-capacity through holes 21a from each
other, and a desirable upper limit is about 6 times the thickness
thereof. When the height is at least about 0.02 time and at most
about 6 times, a sufficient amount of catalyst can be supported on
the protruded portion 24 and the vicinity thereof. Moreover,
strength of the protruded portion 24 becomes sufficient enough to
prevent breakage of the honeycomb structured body due to pressure
or the like of exhaust gases.
[0063] The number of the protruded portions 24 is not particularly
limited, and one protruded portion 24 may be attached to each of
the partition walls 23b that respectively separate adjacent
large-capacity through holes 21a from each other, or a plurality of
them may be attached. Among these structures, a structure in which
a number of protruded portions are formed on each of the partition
walls 23b that respectively separate adjacent large-capacity
through holes 21a from each other so as to prepare a corrugated
surface on each of the partition walls 23b may increase an amount
of droplets retained on each of the partition walls 23b, and
consequently support a sufficient amount of catalyst.
[0064] In the structure in which the recessed portion 34 is formed
on the partition wall 33b, when a base member of the honeycomb
structured body is impregnated with a solution containing a
catalyst or a catalyst material and then taken out, the droplets of
the solution are retained in the recessed portion (groove) 34 by
the use of surface tension of the solution; thereafter, by heating
and drying the resulting base member, a large amount of catalyst
can be supported on the recessed portion 34.
[0065] With respect to the shape of the recessed portion 34,
although not particularly limited, a shape which easily retains
droplets is desirable and, more specifically, a concave shape and a
grooved shape are desirable. Further, a grooved shape continuously
formed from the end on the inlet side of the integral honeycomb
structured body 20 to the end on the outlet side thereof is
desirable. This structure allows a forming process through
extrusion molding.
[0066] With respect to the depth of the recessed portion 34,
although not particularly limited, a desirable lower limit thereof
is about 0.02 time the thickness of the partition wall 33a that
separates adjacent large-capacity through holes 31a from each
other, and a desirable upper limit is about 0.4 time the thickness
thereof. When the depth is at least about 0.02 time and at most
about 0.4 time the thickness, a sufficient amount of catalyst can
be supported on the recessed portion 34 and the vicinity thereof.
Moreover, strength of the partition wall 33a becomes sufficient,
and the honeycomb structured body can be prevented from breaking
due to pressure or the like of exhaust gases.
[0067] The number of the recessed portions 34 is not particularly
limited, and one recessed portion 34 may be formed at each of the
partition walls 33a that respectively separate adjacent
large-capacity through holes 31a from each other, or a plurality of
them may be formed.
[0068] The thickness of the partition wall 23b, 33b that separates
adjacent large-capacity through holes 21a, 31a from each other is
not particularly limited, and the lower limit thereof is desirably
about 0.2 mm, and the upper limit thereof is desirably about 1.2
mm. When the thickness is at least about 0.2 mm and at most about
1.2 mm, a sufficient amount of catalyst can be supported on the
partition wall 23b, 33b that separates adjacent large-capacity
through holes 21a, 31a from each other, and strength in the
integral honeycomb structured body 20, 30 becomes sufficient.
Moreover, since the gas permeability of the partition wall 23b that
separates adjacent large-capacity through holes 21a from each other
is not easily reduced, a subsequent reduction is also difficult to
occur in the exhaust gas purifying (converting) performance.
Therefore, it also becomes difficult for the pressure loss of the
integral honeycomb structured body 20, 30 to increase.
[0069] The thickness of the partition wall 23a, 33a that separates
adjacent large-capacity through hole 21a, 31a and small-capacity
through hole 21b, 31b is not particularly limited, and the lower
limit thereof is desirably about 0.2 mm, and the upper limit
thereof is desirably about 1.2 mm. When the thickness is at least
about 0.2 mm and at most about 1.2 mm, a sufficient amount of
catalyst can be supported on the partition wall 23a, 33a that
separates adjacent large-capacity through hole 21a, 31a and
small-capacity through hole 21b, 31b, and strength of the integral
honeycomb structured body 20, 30 becomes sufficient. Moreover,
since the gas permeability of the partition wall 23a, 33a that
separates adjacent large-capacity through hole 21a, 31a and
small-capacity through hole 21b, 31b is not easily reduced, a
subsequent reduction is also difficult to occur in the exhaust gas
purifying (converting) performance. Therefore, it also becomes
difficult for the pressure loss of the integral honeycomb
structured body 20, 30 to increase.
[0070] Here, the partition wall 23b, 33b that separates adjacent
large-capacity through holes 21a, 31a from each other is desirably
made thicker than the partition wall 23a, 33a that separates
adjacent large-capacity through hole 21a, 31a and small-capacity
through hole 21b, 31b. By making the partition wall 23b, 33b thick,
it becomes possible to support a large amount of catalyst on the
partition wall 23b, 33b. Since the partition wall 23b, 33b is the
partition wall that separates inlet-side through holes from each
other, the influences on the pressure loss is small even when the
thickness thereof is increased so as to support a large amount of
catalyst thereon.
[0071] In the integral honeycomb structured body, since a selective
catalyst supporting portion used for selectively supporting a
catalyst is formed on the partition wall that separates adjacent
large-capacity through holes from each other, exhaust gases are
first allowed to flow into the partition wall having no selective
catalyst supporting portion, that is, the partition wall (partition
wall B) that separates adjacent large-capacity through hole and
small-capacity through hole, and particulates accumulate on the
partition wall.
[0072] The exhaust gases are also allowed to flow into the
partition wall (partition wall A) that separates adjacent
large-capacity through holes from each other since the pressure
loss is higher after a certain degree of particulates accumulate on
the partition wall (partition wall B) that separates adjacent
large-capacity through hole and small-capacity through hole. In
particular, when regenerating the filter, HC, CO and the like in
the exhaust gases are oxidized, and heat is generated through the
oxidizing reaction to cause a temperature rise in the filter, so
that the particulates accumulated thereon are easily burned.
[0073] After the particulates are burned, the pressure loss is
lowered to allow the exhaust gases to flow into the partition wall
B. Thereafter, the above-mentioned processes are repeated.
[0074] Therefore, the partition wall A has a function (heat
supplying function) of increasing the temperature by supplying heat
to the filter, and the partition wall B has a function (pressure
loss increase suppressing function) of suppressing an increase in
the pressure loss in the filter by allowing the exhaust gases to
pass through at the time of both particulate accumulation and
burning. Here, since the partition wall A is a partition wall that
hardly lets exhaust gases pass through inherently, this partition
wall is less likely to contribute to an increase in the pressure
loss even when a catalyst that needs to be supported in a large
amount, such as NOx absorbing catalyst, is supported. Moreover,
when the particulates are burned to generate ashes, since the
partition wall A tends to allow the burning of the particulates on
the catalyst, the ashes accumulate on the partition wall A while
being adhered thereto. However, since the partition wall A is a
partition wall that hardly contributes to an increase in the
pressure loss as described earlier, the pressure loss hardly occurs
even when the ashes deposit thereon.
[0075] Moreover, the ashes deposited on the partition wall A also
prevent a temperature drop on the partition wall A to secure the
heat supplying function. On the other hand, the ashes on the
partition wall B, generated through the burning of particulates due
to heat supplied from the partition wall A, are easily separated
since the amount of the catalyst adhered to the surface of the
partition wall B is small, and easily scattered toward the rear of
the filter by the passing exhaust gases and deposited thereon.
Thus, it is possible to suppress an increase in the pressure loss
due to the partition wall B.
[0076] In the integral honeycomb structured body of the present
invention, a catalyst is supported at least on the selective
catalyst supporting portion. Here, the catalyst may of course be
supported on a portion other than the selective catalyst supporting
portion, and is desirably supported on the partition wall inside
the large-capacity through holes.
[0077] With respect to the catalyst, although not particularly
limited, those which can reduce activating energy of burning
particulates or can convert toxic gas components in exhaust gases
such as CO, HC and NOx are desirably used, and examples thereof may
include noble metals such as platinum, palladium and rhodium, and
the like. Among these, a so-called three-way catalyst, made from
platinum, palladium and rhodium, is desirably used. Moreover, in
addition to the noble metal, an element, such as an alkali metal
(Group 1 in Element Periodic Table), an alkali earth metal (Group 2
in Element Periodic Table), a rare-earth element (Group 3 in
Element Periodic Table) and a transition metal element may be
supported thereon.
[0078] The above-mentioned catalyst may be supported on the surface
of each of pores inside the partition wall, or may be supported on
the partition wall with a certain thickness. Moreover, the
above-mentioned catalyst may be supported on the surface of the
partition wall and/or the surface of each of pores uniformly, or
may be supported on a certain fixed place thereof in a biased
manner. Here, the same is true for the partition wall that
constitutes the selective catalyst supporting portion.
[0079] Among these, the catalyst is desirably supported on the
surface of the partition wall, and a large amount of the catalyst
is more desirably supported on the surface of the selective
catalyst supporting portion. This arrangement easily makes the
catalyst and particulates in contact with each other, thereby
making it possible to carry out the purifying (converting) process
of exhaust gases effectively.
[0080] Moreover, when applying the catalyst to the integral
honeycomb structured body, it is desirable to apply the catalyst
after the surface thereof is coated with a support member such as
alumina. With this arrangement, the specific surface area is made
greater so that the degree of dispersion of the catalyst is
improved and the reaction sites of the catalyst are increased.
Since it is possible to prevent sintering of the catalyst metal by
the support member, the heat resistance of the catalyst is also
improved. In addition, it becomes possible to reduce the pressure
loss.
[0081] The integral honeycomb structured body in which the catalyst
is supported is allowed to function as a filter capable of
collecting particulates in exhaust gases, and also to function as a
catalyst converter for converting CO, HC, NOx and the like
contained in exhaust gases.
[0082] Here, the integral honeycomb structured body of the present
invention is allowed to function as a gas purifying (converting)
device in the same manner as conventionally known DPFs (Diesel
Particulate Filters) with a catalyst. Therefore, with respect to
the case where the integral honeycomb structured body of the
present invention is used as a catalyst supporting member, detailed
description of the functions thereof is omitted.
[0083] Desirably, the integral honeycomb structured body is mainly
made from a porous ceramic material, and examples of the material
may include: nitride ceramics such as aluminum nitride, silicon
nitride, boron nitride and titanium nitride; carbide ceramics such
as silicon carbide, zirconium carbide, titanium carbide, tantalum
carbide and tungsten carbide; oxide ceramics such as alumina,
zirconia, cordierite, mullite and silica; and the like. Moreover,
the integral honeycomb structured body 20 may be made of two or
more kinds of materials such as: a composite material of silicon
and silicon carbide; or aluminum titanate.
[0084] With respect to the particle diameter of the ceramic
material to be used upon manufacturing the integral honeycomb
structured body, although not particularly limited, those materials
that are less likely to shrink in the succeeding firing process are
desirably used, and for example, those materials, prepared by
mixing 100 parts by weight of powder having an average particle
diameter of at least about 0.3 .mu.m and at most about 50 .mu.m
with at least about 5 parts by weight and at most about 65 parts by
weight of powder having an average particle diameter of at least
about 0.1 .mu.m and at most about 1.0 .mu.m, are desirably used. By
mixing ceramic powders having the above-mentioned particle
diameters at the above-mentioned blending ratios, an integral
honeycomb structured body made from porous ceramics can be
manufactured.
[0085] Here, the plugs and the partition wall constituting the
integral honeycomb structured body are desirably made from the same
porous ceramic material. This arrangement makes it possible to
increase the bonding strength between the two members, and by
adjusting the porosity of the plugs in the same manner as that of
the partition wall, it is possible to take the matching of the
coefficient of thermal expansion of the partition wall and the
coefficient of thermal expansion of the plugs. Thus, it becomes
possible to prevent the occurrence of a gap between the plugs and
the partition wall and the occurrence of a crack in the plugs or in
the partition wall at a portion which contacts the plug due to a
thermal stress that is exerted upon production as well as upon
use.
[0086] Although not particularly limited, the lower limit of the
porosity of the integral honeycomb structured body is desirably
about 20%, and the upper limit thereof is desirably about 80%. When
the porosity is at least about 20% and at most about 80%, the
honeycomb structured body 20 is less susceptible to clogging and
breakage of the honeycomb structured body due to degradation in the
strength thereof can be prevented.
[0087] Here, the above-mentioned porosity can be measured through
known methods, such as a mercury injection method, Archimedes
method and a measuring method using a scanning electron microscope
(SEM).
[0088] The lower limit of the average pore diameter of the integral
honeycomb structured body is desirably about 1 .mu.m, and the upper
limit thereof is desirably about 100 .mu.m. When the average pore
diameter is at least about 1 .mu.m and at most about 100 .mu.m, it
becomes difficult for particulates to clog the pore. Moreover,
since particulates can surely be collected without passing through
the pores, the integral honeycomb structured body can function as a
filter.
[0089] The integral honeycomb structured body shown in FIGS. 1A to
1C has an approximately square pillar shape. However, the shape of
the integral honeycomb structured body of the present invention is
not particularly limited as long as it has a pillar shape, and, for
example, pillar shapes having a shape such as a polygonal shape, a
round shape, an elliptical shape and a sector shape, in the
cross-section perpendicular to the longitudinal direction, may be
used.
[0090] Moreover, in the integral honeycomb structured body of the
present invention, the through holes are constituted by two types
of through holes, that is, large-capacity through holes having a
relatively large area on the cross section perpendicular to the
longitudinal direction, with ends on the outlet side of the
integral honeycomb structured body being sealed by plugs, and
small-capacity through holes having a relatively small area on the
cross section with ends on the inlet side of the integral honeycomb
structured body being sealed by the plugs.
[0091] In the case where a filter for purifying (converting)
exhaust gases that has collected particulates and increased the
pressure loss is regenerated, the particulates are burned. In
addition to carbon and the like that are burned and disappear, the
particulates contain metal and the like that are burned to form
oxides and left as ashes in the filter for purifying (converting)
exhaust gases. Since the ashes normally remain at portions closer
to the outlet of the filter for purifying (converting) exhaust
gases, the through holes that serve as filters for purifying
(converting) exhaust gases are filled with ashes starting from a
portion closer to the outlet of the filter for purifying
(converting) exhaust gases, and the capacity of the portion filled
with the ashes gradually increases, while the capacity (area) of a
portion capable of functioning as the filter for purifying
(converting) exhaust gases gradually decreases. When the amount of
accumulated ashes has become too much, the through holes are no
longer allowed to function as the filter. Therefore, the resulting
filter is taken out of the exhaust pipe and subjected to a reverse
washing process to remove the ashes from the filter for purifying
(converting) exhaust gases, or the filter for purifying
(converting) exhaust gases is discarded.
[0092] In comparison with another integral honeycomb structured
body in which the capacity of the inlet-side through holes and the
capacity of the outlet-side through holes are the same, the
integral honeycomb structured body of the present invention has a
smaller ratio of reduction in the capacity (area) of the portion
that functions as the exhaust gas purifying (converting) filter
even after ashes accumulate, so that the pressure loss caused by
the ashes becomes smaller.
[0093] Moreover, in the case where the particulates are burned to
generate ashes, since the particulates tend to be burned on the
catalyst on the partition wall A, the ashes tend to be accumulated
while being adhered to the partition wall A. In this case, however,
since the partition wall A is prepared as a partition wall that
hardly causes an increase in pressure loss, the accumulation of
ashes hardly causes an increase in pressure loss.
[0094] Here, the accumulated ashes on the partition wall A also
have functions of preventing a temperature drop on the partition
wall A and of securing a heat supplying function. On the other
hand, ashes on the partition wall B, generated through the burning
of particulates due to heat supplied from the partition wall A, are
easily separated since only a small amount of catalyst is adhered
to the surface of the partition wall B, and scattered toward the
rear of the filter by passing exhaust gases and deposited thereon,
so that it is possible to suppress an increase in pressure loss
caused by the partition wall B.
[0095] Thus, the integral honeycomb structured body of the present
invention makes it possible to prolong a period of time until the
reverse washing and the like is required, and consequently to
provide a longer service life as the filter for purifying
(converting) exhaust gases. Consequently, it becomes possible to
greatly cut maintenance costs required for reverse washing,
exchanging members and the like.
[0096] In recent years, in the honeycomb structured body on which a
catalyst is supported, a phenomenon in which ashes are deposited on
the coating layer of the catalyst has been reported. Even in such a
deposition state of ashes, the integral honeycomb structured body
of the present invention, which has ashes deposited on the
partition wall that is inherently less likely to contribute to an
increase in pressure loss, can prevent an increase in pressure loss
due to accumulation of ashes.
[0097] In the integral honeycomb structured body of the present
invention having the structure as shown in FIGS. 1A to 1C, the
shape of a cross section perpendicular to the longitudinal
direction of the large-capacity through hole and/or small-capacity
through hole is desirably formed into a polygonal shape. Even when
the area of the partition wall in across-section perpendicular to
the longitudinal direction of the honeycomb structured body is
reduced to increase the aperture ratio, this polygonal shape makes
it possible to achieve a honeycomb structured body that has an
excellent durability and has a long service life. Among polygonal
shapes, a polygon having four or more angles is desirably used and,
more desirably, at least one of the angles is an obtuse angle. With
this arrangement, it becomes possible to reduce a pressure loss
caused by friction of exhaust gases upon passing through the
through holes. Here, only the cross section of the large-capacity
through holes may be a polygon, such as a quadrangle, a pentagon, a
trapezoid and an octagon, or only the cross section of the
small-capacity through holes may be the above-mentioned polygon, or
both of them may be a polygon. In particular, the shape of across
section perpendicular to the longitudinal direction of the
large-capacity through holes is desirably an octagonal shape, with
the shape of the cross section of the small-capacity through holes
being desirably a quadrangle shape.
[0098] In the integral honeycomb structured body of the present
invention, the ratio of the sum of areas on the cross section
perpendicular to the longitudinal direction of the large-capacity
through holes to the sum of areas on the cross section of the
small-capacity through holes (total cross-sectional areas of
large-capacity through holes/total cross-sectional areas of
small-capacity through holes; hereinafter, also referred to as
ratio of aperture ratios) desirably has a lower limit value of
about 1.5, and the upper limit value of about 2.7. When the ratio
of areas is less than about 1.5, the effects of preparing the
large-capacity through holes and the small-capacity through holes
are hardly obtained. On the other hand, the ratio of areas
exceeding about 2.7 makes the capacity of the small-capacity
through holes too small, and the pressure loss prior to collecting
particulates may become too large.
[0099] In the integral honeycomb structured body of the present
invention, the vicinity of each of corners on the cross section
perpendicular to the longitudinal direction of the large-capacity
through holes and/or the small-capacity through holes is desirably
formed by a curved line. By forming the corner into a curved line,
it becomes possible to prevent a stress from concentrating on the
corner portions of the through holes and the subsequent occurrence
of cracks, and also to reduce a pressure loss due to friction
caused by exhaust gases passing through the through holes.
[0100] In the integral honeycomb structured body of the present
invention, the distance between centers of gravity on a cross
section perpendicular to the longitudinal direction of adjacent
large-capacity through holes is desirably equal to the distance
between centers of gravity on a cross section perpendicular to the
longitudinal direction of adjacent small-capacity through holes.
With this arrangement, upon regenerating, heat is uniformly
dispersed so that the temperature distribution is easily made
uniform. Thus, it becomes possible to provide a honeycomb
structured body that has an excellent durability and is less likely
to generate cracks due to a thermal stress even after repetitive
uses for a long time.
[0101] In the present invention, the term "the distance between
centers of gravity on a cross section perpendicular to the
longitudinal direction of adjacent large-capacity through holes"
represents the smallest distance between the center of gravity on a
cross section perpendicular to the longitudinal direction of one
large-capacity through hole and the center of gravity on the cross
section of another large-capacity through hole. The term "the
distance between centers of gravity on a cross section of adjacent
small-capacity through holes" represents the smallest distance
between the center of gravity on a cross section perpendicular to
the longitudinal direction of one small-capacity through hole and
the center of gravity on the cross section of another
small-capacity through hole.
[0102] Moreover, in the integral honeycomb structured body 20 shown
in FIGS. 1A and 1B, the large-capacity through holes 21a and the
small-capacity through holes 21b are alternately arranged in the
vertical direction as well as in the horizontal direction with a
partition wall 23 interposed therebetween, and, in each of the
directions, the center of gravity on a cross section perpendicular
to the longitudinal direction of each of the large-capacity through
holes 21a and the center of gravity on a cross section
perpendicular to the longitudinal direction of each of the
small-capacity through holes 21b are located on a straight
line.
[0103] Therefore, "the distance between centers of gravity on a
cross section perpendicular to the longitudinal direction of
adjacent large-capacity through holes" and "the distance between
centers of gravity on the cross section of adjacent small-capacity
through holes" respectively refer to a distance between centers of
gravity of large-capacity through holes 21a that are diagonally
adjacent to each other and small-capacity through holes 21b that
are diagonally adjacent to each other in a cross section
perpendicular to the longitudinal direction of the integral
honeycomb structured body 20 of the present invention.
[0104] In the integral honeycomb structured body of the present
invention, although not particularly limited, the number of the
large-capacity through holes and the number of the small-capacity
through holes are desirably set to substantially the same number.
With this arrangement, it is possible to minimize the partition
wall that hardly participates in filtration of exhaust gases, and
consequently to prevent the pressure loss caused by friction due to
gases passing through the inlet-side through holes and/or friction
due to gases passing through the outlet-side through holes from
rising over the necessary level. For example, in comparison with a
honeycomb structured body 100 in which the number of the
large-capacity through holes 101 and the number of the
small-capacity through holes 102 are substantially set to about
1:2, as shown in FIG. 2, the structure in which the numbers of the
respective through holes are substantially the same number makes it
possible to reduce the pressure loss caused by friction due to
gases passing through the outlet-side through holes, and
consequently to reduce the pressure loss with respect to the
honeycomb structured body as a whole.
[0105] The following description will discuss specific examples of
structures of the large-capacity through holes and the
small-capacity through holes on the cross section perpendicular to
the longitudinal direction of the integral honeycomb structured
body of the present invention.
[0106] FIGS. 3A to 3D and FIGS. 4A to 4F are cross-sectional views
each of which schematically shows a cross section perpendicular to
the longitudinal direction in the integral honeycomb structured
body of the present invention; and FIG. 3E is a cross-sectional
view that schematically shows a cross section perpendicular to the
longitudinal direction in a conventional integral honeycomb
structured body.
[0107] In the integral honeycomb structured body 110 shown in FIG.
3A, the ratio of aperture ratios is about 1.55; in the integral
honeycomb structured body 120 shown in FIG. 3B, the ratio is about
2.54; in the integral honeycomb structured body 130 shown in FIG.
3C, the ratio is about 4.45; and in the integral honeycomb
structured body 140 shown in FIG. 3D, the ratio is about 6.00.
Moreover, in FIGS. 4A, 4C and 4E, all the ratios of aperture ratios
are about 4.45, and in FIGS. 4B, 4D and 4F, all the ratios of
aperture ratios are about 6.00.
[0108] Here, in the case where the ratio of aperture ratios is
great as indicated by the integral honeycomb structured body 140 of
FIG. 3D, the initial pressure loss tends to become too high since
the capacity of the small-capacity through holes 141b forming the
group of outlet-side through holes becomes too small.
[0109] In the integral honeycomb structured bodies 110, 120, 130,
140 shown in FIGS. 3A to 3D, protruded portions 114, 124, 134, 144
are formed on the partition walls that respectively separate the
large-capacity through holes 111a, 121a, 131a, 141a from one
another. The cross-sectional shape of each of the large-capacity
through holes 111a, 121a, 131a, 141a, from which each of the
protruded portions 114, 124, 134, 144 is omitted, is an octagon.
The cross-sectional shape of each of the small-capacity through
holes 111b, 121b, 131b, 141b is a quadrangle (square). The
large-capacity through holes 111a, 121a, 131a, 141a and the
small-capacity through holes 111b, 121b, 131b, 141b are alternately
arranged. Here, in the integral honeycomb structured bodies shown
in FIGS. 3A to 3D, by changing the cross-sectional area of the
small-capacity through holes and also slightly changing the
cross-sectional shape of the large-capacity through holes, it is
possible to easily vary the ratio of aperture ratios arbitrarily.
In the same manner, with respect to the integral honeycomb
structured body shown in FIG. 4, it is also possible to easily vary
the ratio of aperture ratios arbitrarily. Moreover, as shown in
FIGS. 3A to 3D, it is desirable to provide chamfered portions on
corner portions on the periphery of the integral honeycomb
structured body of the present invention.
[0110] Here, in an integral honeycomb structured body 150 shown in
FIG. 3E, both of the cross-sectional shapes of inlet-side through
holes 152a and outlet-side through holes 152b are quadrangle
shapes, and alternately arranged respectively.
[0111] In integral honeycomb structured bodies 160, 260 shown in
FIGS. 4A and 4B, protruded portions 164, 264 are formed on the
partition walls that respectively separate the large-capacity
through holes 161a, 261a. The cross-sectional shape of each of the
large-capacity through holes 161a, 261a, from which each of the
protruded portions 164, 264 is omitted, is a pentagon, and in this
shape, three angles thereof are set to approximately right angles.
The cross-sectional shape of each of the small-capacity through
holes 161b, 261b is a quadrangle and the small-capacity through
holes are allowed to respectively occupy portions of a larger
quadrangle that diagonally face each other. In integral honeycomb
structured bodies 170, 270 shown in FIGS. 4C and 4D, protruded
portions 174, 274 are formed on the partition walls that
respectively separate the large-capacity through holes 171a, 271a.
Here, the cross-sectional shapes of the integral honeycomb
structured bodies 170, 270 shown in FIGS. 4C and 4D are modified
shapes of the cross-sectional shapes shown in FIGS. 3A to 3D, and
the shape is formed by expanding a partition wall commonly
possessed by each of the large-capacity through holes 171a, 271a
and each of the small-capacity through holes 171b, 271b toward the
small-capacity through hole side with a predetermined curvature.
This curvature is optionally set, and the curved line forming the
partition wall may correspond to, for example, a 1/4 of a circle.
In this case, the above-mentioned ratio of aperture ratios is 3.66.
Therefore, in the integral honeycomb structured bodies 170, 270,
shown in FIGS. 4C and 4D, the area of the cross section of each of
the small-capacity through holes 171b, 271b is made further smaller
compared to the case in which the curved line forming the partition
wall corresponds to a 1/4 of a circle. In integral honeycomb
structured bodies 180, 280 shown in FIGS. 4E and 4F, protruded
portions 184, 284 are formed on the partition walls that
respectively separate the large-capacity through holes 181a, 281a.
The cross-sectional shape of each of the large-capacity through
holes 181a, 281a, from which each of the protruded portions 184,
284 is omitted, as well as the cross-sectional shape of each of the
small-capacity through holes 181b, 281b, is a quadrangle
(rectangle). When two of the large-capacity through holes and two
of the small-capacity through holes are combined together, an
approximately square shape is formed.
[0112] Other specific examples of structures of the large-capacity
through holes and the small-capacity through holes in the cross
section perpendicular to the longitudinal direction of the integral
honeycomb structured body of the present invention may include an
integral honeycomb structured body 190 as shown in FIG. 5 having
large-capacity through holes 191a, small-capacity through holes
191b and protruded portions 194 and the like.
[0113] Only a single integral honeycomb structured body of the
present invention may be used as an integral-type filter. More
desirably, a plurality of them may be combined together through a
sealing material layer, and used as an aggregated-type filer. The
aggregated-type filter makes it possible to reduce a thermal stress
by the sealing material layer to improve the heat resistance of the
filter. Further, the size and the like of the filter can be freely
adjusted by increasing or decreasing the number of the integral
honeycomb structured bodies.
[0114] Here, both of the integral-type filter and the
aggregated-type filter have the same functions.
[0115] In the integral-type filter formed by the integral honeycomb
structured body of the present invention, an oxide ceramic material
such as cordierite is normally used as its material. This material
makes it possible to cut manufacturing costs, and since this
material has a comparatively small coefficient of thermal
expansion, it is possible to make the filter less likely to receive
damage due to a thermal stress that is exerted during production as
well as during use.
[0116] In the integral-type filter formed by the integral honeycomb
structured body of the present invention, although not shown in
FIGS. 1A to 1C, a sealing material layer, made from a material that
hardly lets gases pass through in comparison with the integral
honeycomb structured body of the present invention, is desirably
formed on the peripheral face thereof in the same manner as the
aggregated honeycomb structured body of the present invention which
will be described later. In the case where the sealing material
layer is formed on the peripheral face, the integral honeycomb
structured body of the present invention is compressed by the
sealing material layer, so that it is possible to increase the
strength, and also to prevent isolation of ceramic particles due to
occurrence of cracks.
[0117] In accordance with the integral honeycomb structured body of
the present invention, since the selective catalyst supporting
portion is formed on the partition wall that separates the adjacent
through holes constituting the group of through holes, a partition
wall on which a large amount of catalyst is supported (hereinafter,
referred to as partition wall A) and the other partition wall
(hereinafter, referred to as partition wall B) are allowed to exert
different functions. In other words, the partition wall A has a
function of supplying the filter with heat generated through
oxidizing reactions of HC, CO and the like in exhaust gases by the
catalyst to increase the temperature (heat supplying function). The
partition wall B has a function of letting exhaust gases pass
through during both of the particulate accumulating process and the
particulate burning process so as to prevent the pressure loss of
the filter from increasing (suppressing function of pressure loss
increase). Here, since the partition wall A is a partition wall
that hardly lets exhaust gases pass through inherently, this
partition wall is less likely to contribute to an increase in the
pressure loss even when a catalyst that needs to be supported in a
large amount, such as NOx absorbing catalyst, is supported.
Moreover, when the particulates are burned to generate ashes, the
ashes are accumulated on the partition wall A while being adhered
thereto since the partition wall A tends to allow the burning of
the particulates on the catalyst. However, since the partition wall
A is a partition wall that hardly causes an increase in the
pressure loss as described earlier, the pressure loss hardly occurs
even when the ashes are deposited thereon.
[0118] Moreover, the ashes deposited on the partition wall A also
prevent a temperature drop on the partition wall A to maintain the
heat supplying function. On the other hand, on the partition wall
B, the ashes, generated through the burning of particulates due to
heat supplied from the partition wall A, are easily separated since
the amount of the catalyst adhered to the surface of the partition
wall B is small, and easily scattered toward the rear of the filter
by the passing exhaust gases and deposited therein. Thus, it is
possible to suppress an increase in the pressure loss due to the
partition wall B.
[0119] Furthermore, since an increased amount of catalyst is
supported, the purifying (converting) function for exhaust gases is
improved in addition to the above-mentioned functions, and
depending on the amount of catalyst, it becomes possible to burn
and remove the particulates without a high-temperature regenerating
process, and consequently to suppress an increase in the pressure
loss upon collecting particulates. Moreover, since a partition wall
which separates inlet-side through holes from each other hardly
allows exhaust gases to flow therein, it gives only little
influences to the pressure loss, even when its shape, the amount of
the supported catalyst and the like are changed.
[0120] When the selective catalyst supporting portion is prepared
as a protruded portion and/or a recessed portion formed on the
partition wall that separates adjacent through holes constituting
the group of large-capacity through holes, a catalyst is easily
supported on the selective catalyst supporting portion selectively.
In the case where the protruded portion, formed at the selective
catalyst supporting portion, is designed to have a height of at
least about 0.02 time and at most about 6 times the thickness of
the partition wall that separates adjacent through holes
constituting the group of large-capacity through holes, or in the
case where the recessed portion, formed at the selective catalyst
supporting portion, is designed to have a depth of at least about
0.02 time and at most about 0.4 time the thickness of the partition
wall that separates adjacent through holes constituting the group
of large-capacity through holes, the catalyst is easily supported
on the selective catalyst supporting portion selectively, thereby
making it possible to prevent damages to the protruded portion due
to pressure of exhaust gases and the like and the subsequent
damages to the partition wall.
[0121] In the integral honeycomb structured body of the present
invention, if the cross-sectional shape perpendicular to the
longitudinal direction of the through holes that constitute the
group of large-capacity through holes and/or the through holes that
constitute the group of small-capacity through holes is a polygonal
shape, even when the area of the partition wall on the cross
section perpendicular to the longitudinal direction is reduced to
increase the aperture ratio in order to reduce the pressure loss,
it becomes possible to achieve a honeycomb structured body having
superior durability and a long service life. Moreover, in the case
where the cross-sectional shape perpendicular to the longitudinal
direction of the through holes that constitute the group of
large-capacity through holes is an octagonal shape while the
cross-sectional shape perpendicular to the longitudinal direction
of the through holes that constitute the group of small-capacity
through holes is a quadrangular shape, it becomes possible to
achieve a honeycomb structured body having further superior
durability and a longer service life.
[0122] Here, in the present invention, the aperture ratio refers to
a ratio of the area of the group of the large-capacity through
holes to the total area of the end faces on the inlet side of the
honeycomb structured body, and is represented by, for example,
percentage (%). In this case, it is defined that the portion
occupied by the sealing material layer is not included in the total
area of the end faces.
[0123] In the integral honeycomb structured body of the present
invention, when a ratio of the sum of areas on a cross section
perpendicular to the longitudinal direction of the through holes
that constitute the group of large-capacity through holes to the
sum of areas on the cross section perpendicular to the longitudinal
direction of the through holes that constitute the group of
small-capacity through holes is in the range of 1.5 to 2.7, it is
possible to suppress an increase in pressure loss upon collecting
particulates by increasing the aperture ratio on the inlet side
relatively, and also to prevent the pressure loss prior to the
particulate collecting process from becoming too high.
[0124] In the integral honeycomb structured body of the present
invention, when, on the cross section perpendicular to the
longitudinal direction, at least one of angles formed by crossing
of the partition wall that separates adjacent through holes
constituting the group of large-capacity through holes and the
partition wall that separates adjacent through holes, one of which
constituting the group of large-capacity through holes and the
other of which constituting the group of small-capacity through
holes, is an obtuse angle, it becomes possible to reduce the
pressure loss.
[0125] In the integral honeycomb structured body of the present
invention, if, on the cross section perpendicular to the
longitudinal direction, the vicinity of each of corners of the
through hole constituting the group of the large-capacity through
holes and/or the through hole constituting the group of the
small-capacity through holes is formed by a curved line, it becomes
possible to prevent stresses from concentrating on each corner of
the through hole, and consequently to prevent occurrence of cracks
as well as to reduce the pressure loss.
[0126] In the integral honeycomb structured body of the present
invention, if the distance between centers of gravity on a cross
section perpendicular to the longitudinal direction of adjacent
through holes constituting the group of the large-capacity through
holes is equal to the distance between centers of gravity on a
cross section perpendicular to the longitudinal direction of
adjacent through holes constituting the group of the small-capacity
through holes, upon regenerating, heat is easily dispersed
uniformly to make a uniform temperature distribution, so that it
becomes possible to provide a honeycomb structured body that is
superior in durability and less likely to generate cracks caused by
thermal stresses even after repetitive uses for a long time.
[0127] The aggregated honeycomb structured body of the present
invention comprises:
[0128] a honeycomb block formed by combining a plurality of the
integral honeycomb structured bodies of the present invention
together through a sealing material layer; and
[0129] a sealing material layer which is formed on the peripheral
face of the honeycomb block,
[0130] wherein the sealing material layer is made from a material
that hardly lets gases pass through in comparison with the integral
honeycomb structured body of the present invention,
[0131] and functions as an aggregated-type filter.
[0132] FIG. 6 is a perspective view that schematically shows one
example of the aggregated honeycomb structured body of the present
invention. In the aggregated honeycomb structured body shown in
FIG. 6, a number of through holes are constituted by a group of
large-capacity through holes being sealed at one of the end
portions of the honeycomb structured body so that the sum of areas
on the cross section perpendicular to the longitudinal direction is
made relatively greater, and a group of small-capacity through
holes being sealed at the other end portion of the honeycomb
structured body so that the some of areas on the cross section is
made relatively smaller.
[0133] As shown in FIG. 6, the aggregated honeycomb structured body
10, which is used as a filter for purifying (converting) exhaust
gases, has a structure in which a plurality of the integral
honeycomb structured bodies 20 are combined together through a
sealing material layer 14 to form a honeycomb block 15, with a
sealing material layer 13 for preventing leakage of exhaust gases
formed on the periphery of the honeycomb block 15. Here, the
sealing material layer 13 is made from a material that hardly lets
gases pass through in comparison with the integral honeycomb
structured body 20.
[0134] Here, in the aggregated honeycomb structured body 10,
silicon carbide, which is superior in thermal conductivity, heat
resistance, mechanical properties, chemical resistance and the
like, is desirably used as a material for constituting the integral
honeycomb structured body 20.
[0135] In the aggregated honeycomb structured body 10, the sealing
material layer 14, which is formed between the integral ceramic
structured bodies 20, desirably serves as an adhesive that bonds a
plurality of the integral ceramic structured bodies 20 to one
another. The sealing material layer 13, on the other hand, which is
formed on the peripheral face of the honeycomb block 15, serves as
a sealing member that prevents exhaust gases that pass through the
through holes from leaking from the peripheral face of the
honeycomb block 15, when the aggregated honeycomb structured body
10 is placed in an exhaust passage in an internal combustion
engine.
[0136] Here, in the aggregated honeycomb structured body 10, the
sealing material layer 13 and the sealing material layer 14 may be
made from the same material, or may be made from different
materials. In the case where the sealing material layer 13 and the
sealing material layer 14 are made from the same material, the
blending ratio of the materials may be the same or different from
each other.
[0137] The sealing material layer 14 may be made from a dense
material or may be made from a porous material so as to allow
exhaust gases to flow therein. However, the sealing material layer
13 is desirably made from a dense material. This is because the
sealing material layer 13 is formed so as to prevent leakage of
exhaust gases from the peripheral face of the ceramic block 15 when
the aggregated honeycomb structured body 10 is placed in an exhaust
passage of an internal combustion engine.
[0138] With respect to the material for forming the sealing
material layer 13 and the sealing material layer 14, examples
thereof are not particularly limited and may include a material
comprising inorganic fibers and/or inorganic particles in addition
to an inorganic binder and an organic binder.
[0139] With respect to the inorganic binder, for example, silica
sol, alumina sol and the like may be used. Each of these may be
used alone or two or more kinds of these may be used in
combination. Among the inorganic binders, silica sol is more
desirably used.
[0140] With respect to the organic binder, examples thereof may
include polyvinyl alcohol, methyl cellulose, ethyl cellulose,
carboxymethyl cellulose and the like. Each of these may be used
alone or two or more kinds of these may be used in combination.
Among the organic binders, carboxymethyl cellulose is more
desirably used.
[0141] With respect to the inorganic fibers, examples thereof may
include ceramic fibers such as silica-alumina, mullite, alumina,
silica and the like. Each of these may be used alone or two or more
kinds of these may be used in combination. Among the inorganic
fibers, silica-alumina fibers are more desirably used.
[0142] With respect to the inorganic particles, examples thereof
may include carbides, nitrides and the like, and specific examples
may include inorganic powder, whiskers and the like made from
silicon carbide, silicon nitride, boron nitride and the like. Each
of these may be used alone, or two or more kinds of these may be
used in combination. Among the inorganic particles, silicon carbide
having an excellent thermal conductivity is desirably used.
[0143] In the case where the integral honeycomb structured body of
the present invention, as it is, is used as a filter for purifying
(converting) exhaust gases as described above, the sealing material
layer that is the same as that of the aggregated honeycomb
structured body of the present invention may be formed on the
peripheral face of the integral honeycomb structured body of the
present invention.
[0144] The aggregated honeycomb structured body 10 shown in FIG. 6
has a cylindrical shape. However, the shape of the aggregated
honeycomb structured body of the present invention is not
particularly limited as long as it is a pillar-shaped body, and may
be, for example, a pillar-shape with a cross-sectional shape
perpendicular to the longitudinal direction being a polygonal
shape, an elliptical shape and the like.
[0145] The aggregated honeycomb structured body of the present
invention may be manufactured by: processes in which, after a
plurality of integral honeycomb structured bodies of the present
invention have been combined together, the peripheral portion
thereof is machined so as to form the cross section perpendicular
to the longitudinal direction into a polygonal shape, a round
shape, an elliptical shape or the like; or processes in which,
after the cross section of the integral honeycomb structured bodies
of the present invention have been preliminarily machined, the
resulting structured bodies are combined together by using an
adhesive so as to form the cross section perpendicular to the
longitudinal direction into a polygonal shape, a round shape, an
elliptical shape or the like. For example, four pillar-shaped
integral honeycomb structured bodies of the present invention, each
having a sector shape on its cross section perpendicular to the
longitudinal direction that is one of four equally divided portions
of a circle, may be combined together to manufacture a cylindrical
aggregated honeycomb structured body of the present invention.
[0146] In accordance with the aggregated honeycomb structured body
of the present invention, the honeycomb structured body has a
structure in which a plurality of the integral honeycomb structured
bodies of the present invention is combined together through a
sealing material layer. Therefore, it is possible to improve the
heat resistance by reducing thermal stresses by using the sealing
material layer, and also to freely adjust the size by increasing or
reducing the number of the integral honeycomb structured bodies of
the present invention.
[0147] Next, the following description will discuss one example of
a manufacturing method for the above-mentioned honeycomb structured
body of the present invention.
[0148] In the case where the honeycomb structured body of the
present invention is an integral-type filter in which the entire
structure is made of a single sintered body, first, an
extrusion-molding process is carried out by using the material
paste mainly composed of the above-mentioned ceramics so that a
ceramic formed body having approximately the same shape as the
integral honeycomb structured body of the present invention with
the selective catalyst supporting portions formed thereon is
manufactured. In this case, for example, metal molds that are used
for extrusion-molding having two types of through holes, that is,
large-capacity through holes and small-capacity through holes, are
selected in accordance with the densities of the through holes.
[0149] Here, the shape of the selective catalyst supporting
portions can be adjusted by changing the shape of the opening
section of a die to be used for the above-mentioned
extrusion-molding.
[0150] Although the material paste is not particularly limited,
material paste which sets the porosity of the integral honeycomb
structured body after the manufacturing process is desirably at
least about 20% and at most about 80%, and, for example, a material
paste prepared by adding a binder, a dispersant solution and the
like to powder made from the above-mentioned ceramics may be
used.
[0151] The above-mentioned binder is not particularly limited, and
examples thereof may include methylcellulose, carboxymethyl
cellulose, hydroxyethyl cellulose, polyethylene glycol, phenol
resins, epoxy resins and the like.
[0152] Normally, the blend ratio of the above-mentioned binder is
desirably at least about 1 part by weight and at most about 10
parts by weight to 100 parts by weight of ceramic powder.
[0153] The above-mentioned dispersant solution is not particularly
limited, and, for example, an organic solvent such as benzene,
alcohol such as methanol, water and the like may be used.
[0154] An appropriate amount of the above-mentioned dispersant
solution is blended so that the viscosity of the material paste is
set in a predetermined range.
[0155] These ceramic powder, binder and dispersant solution are
mixed by an attritor or the like, and sufficiently kneaded by a
kneader or the like, and then extrusion-molded.
[0156] Moreover, a molding auxiliary may be added to the
above-mentioned material paste, if necessary.
[0157] The molding auxiliary is not particularly limited, and
examples thereof may include ethylene glycol, dextrin, fatty acid
soap, polyalcohol and the like.
[0158] Furthermore, a pore-forming agent, such as balloons that are
fine hollow spheres composed of oxide-based ceramics, spherical
acrylic particles or graphite, may be added to the above-mentioned
material paste, if necessary.
[0159] The above-mentioned balloons are not particularly limited
and, for example, alumina balloons, glass micro-balloons, shirasu
balloons, fly ash balloons (FA balloons), mullite balloons and the
like may be used. Among these, fly ash balloons are more desirably
used.
[0160] Next, the above-mentioned ceramic formed body is dried by
using a micro-wave dryer, a hot-air dryer, a dielectric dryer, a
decompression dryer, a vacuum dryer, a freeze dryer or the like to
form a ceramic dried body. Next, a predetermined amount of plug
paste, which forms plugs, is injected into ends on the outlet side
of the large-capacity through holes and ends on the inlet side of
the small-capacity through holes so as to seal the through
holes.
[0161] Although the above-mentioned plug paste is not particularly
limited, the plug paste which sets the porosity of a plug
manufactured through the following processes is desirably at least
about 20% and at most about 80%, and for example, the same material
paste as described above may be used. However, those pastes,
prepared by adding a lubricant, a solvent, a dispersant, a binder
and the like to ceramic powder used as the above-mentioned material
paste, are desirably used. With this arrangement, it becomes
possible to prevent ceramics particles and the like in the plug
paste from settling in the middle of the sealing process.
[0162] Next, the ceramic dried body filled with the plug paste is
subjected to degreasing and firing processes under predetermined
conditions.
[0163] Here, with respect to the degreasing and firing conditions
and the like of the ceramic dried body, it is possible to apply
conditions that have been conventionally used for manufacturing a
filter made from porous ceramics.
[0164] Next, an alumina film having a high specific surface area is
formed on the surface of the ceramic fired body obtained from the
firing process, and a catalyst such as platinum is applied onto the
surface of the alumina film so that an integral honeycomb
structured body of the present invention, which is made from a
porous ceramic material on the surface of which a catalyst is
supported, and formed by a single sintered body as a whole, is
manufactured.
[0165] With respect to the method for forming the alumina film on
the surface of the ceramic fired body, examples thereof may
include: a method in which the ceramic fired body is impregnated
with a solution of a metal compound containing aluminum such as
Al(NO.sub.3).sub.3 and then heated; a method in which the ceramic
fired body is impregnated with a slurry solution containing
.gamma.-alumina powder, which has a high surface area and is
obtained by pulverizing .gamma.-alumina, and then heated; and the
like.
[0166] With respect to the method for applying a co-catalyst and
the like to the alumina film, examples thereof may include a method
in which the ceramic fired body is impregnated with a solution of a
metal compound containing a rare-earth element, such as
Ce(NO.sub.3).sub.3, and then heated, and the like.
[0167] With respect to the method for applying a catalyst to the
alumina film, examples thereof may include a method in which the
ceramic fired body is impregnated with a solution of diamine
dinitro platinum nitric acid ([Pt
(NH.sub.3).sub.2(NO.sub.2).sub.2]HNO.sub.3) and the like and then
heated, and the like.
[0168] Moreover, in the case where the honeycomb structured body of
the present invention is an aggregated honeycomb structured body 10
which is constituted by a plurality of integral honeycomb
structured bodies 20 combined with one another through a sealing
material layer 14 as shown in FIG. 6, an adhesive paste to form a
sealing material layer 14 is applied with an even thickness, and
other integral honeycomb structured bodies 20 coated with the
adhesive paste are sequentially laminated thereon. A laminated body
of a square-pillar shaped integral honeycomb structured bodies 20
having a predetermined size is thus manufactured.
[0169] Here, with respect to the material for forming the adhesive
paste, the detailed description is omitted, since the explanation
thereof has already been given.
[0170] Next, the laminated body of the integral honeycomb
structured bodies 20 is heated so that the adhesive paste layer is
dried and solidified to form the sealing material layer 14, and, by
using a diamond cutter or the like, the peripheral portion thereof
is then cut into a shape as shown in FIG. 6 so that a honeycomb
block 15 is manufactured.
[0171] Then, a sealing material layer 13 is formed on the
peripheral portion of the honeycomb block 15 by using the adhesive
paste so that the aggregated-type filter 10 of the present
invention, constituted by a plurality of integral honeycomb
structured bodies 20 combined together through a sealing material
layer 14, is manufactured.
[0172] Here, when manufacturing the aggregated filter 10 of the
present invention, the formation of the alumina film, the
application of the catalyst and the like may be carried out after
the formation of the honeycomb block 15, without carrying out these
processes after the formation of the ceramic fired body.
[0173] Although not particularly limited, the honeycomb structured
body of the present invention is desirably applied to an exhaust
gas purifying (converting) device for use in vehicles.
[0174] FIG. 7 is a cross-sectional view that schematically shows
one example of an exhaust gas purifying (converting) device of a
vehicle in which the honeycomb structured body of the present
invention is installed.
[0175] As shown in FIG. 7, an exhaust gas purifying (converting)
device 600 is mainly constituted by a honeycomb structured body 60,
a casing 630 that covers the external portion of the honeycomb
structured body 60, a holding sealing material 620 that is placed
between the honeycomb structured body 60 and the casing 630 and a
heating means 610 placed at the exhaust gas inlet side of the
honeycomb structured body 60. An introducing pipe 640, which is
connected to an internal combustion engine such as an engine, is
connected to one end of the casing 630 on the exhaust gas inlet
side, and an exhaust pipe 650, which is connected to the outside,
is connected to the other end of the casing 630. In FIG. 7, arrows
show flows of exhaust gases.
[0176] Moreover, in FIG. 7, the honeycomb structured body 60 may be
the integral honeycomb structured bodies 20,30 shown in FIGS. 1A to
1C or the aggregated honeycomb structured body 10 shown in FIG.
6.
[0177] In the exhaust gas purifying (converting) device 600 having
the above-mentioned constitution, exhaust gases, discharged from
the internal combustion engine such as an engine, are directed into
the casing 630 through the introducing pipe 640, and allowed to
flow into the honeycomb structured body 60 through the
large-capacity through holes 21a and to pass through the portions
of the partition wall 23. Then, the exhaust gases are purified,
with particulates thereof being collected in the partition wall 23,
and are then discharged to the outside of the honeycomb structured
body 60 from the small-capacity through holes 21b, and discharged
outside through the exhaust pipe 650.
[0178] In the exhaust gas purifying (converting) device 600, after
a large quantity of particulates accumulate on the partition wall
of the honeycomb structured body 60 to cause an increase in
pressure loss, the honeycomb structured body 60 is subjected to a
regenerating process.
[0179] In the regenerating process, gases, heated by using a
heating means 610, are allowed to flow into the through holes of
the honeycomb structured body 60, so that the honeycomb structured
body 60 is heated to burn and eliminate the particulates deposited
on the partition wall. Moreover, the particulates may be burned and
eliminated by using a post-injection system. In addition to these
methods, a filter to which an oxide catalyst is applied may be
placed at a portion of the introducing pipe 640 in front of the
casing 630, or a filter to which an oxide catalyst is applied may
be placed on the exhaust gas inlet side of the heating means 610
inside the casing 630.
[0180] In the honeycomb structured body of the present invention,
when the honeycomb structured body is used for an exhaust gas
purifying (converting) device for use in a vehicle, it is possible
to improve the purifying (converting) performance for exhaust
gases, and also to suppress an increase in pressure loss upon
collecting particulates to prolong the period up to the
regenerating process, to improve the heat resistance and also to
freely adjust the size and the like.
EXAMPLES
[0181] Referring to the figures, the following description will
discuss the present invention in detail by means of examples.
However, the present invention is not intended to be limited by
these examples.
Example 1
[0182] (1) Powder of .alpha.-type silicon carbide having an average
particle diameter of 10 .mu.m (60% by weight) and powder of
.beta.-type silicon carbide having an average particle diameter of
0.5 .mu.m (40% by weight) were wet-mixed, and to 100 parts by
weight of the resulting mixture were added and kneaded 5 parts by
weight of an organic binder (methyl cellulose) and 10 parts by
weight of water to obtain a mixed composition. Next, after adding a
slight amount of a plasticizer and a lubricant and further
kneading, the resulting mixture was extrusion-molded, so that a raw
molded product having a cross-sectional shape that was
approximately the same cross-sectional shape shown in FIG. 3A, with
an aperture ratio on the inlet side of 37.97% and a ratio of
aperture ratios of 1.55, was manufactured. The thickness of the
partition wall separating adjacent large-capacity through hole and
small-capacity through hole was 0.3 mm, the thickness of the
partition wall separating adjacent large-capacity through holes
from each other was 0.6 mm, and the height of each protruded
portion formed on the partition wall separating adjacent
large-capacity through holes from each other was 0.1 mm.
[0183] Next, after drying the above-mentioned raw molded product by
using a microwave drier or the like to form a ceramic dried body,
predetermined through holes were filled with a plug paste having
the same composition as the raw molded product.
[0184] After having been again dried by using a drier, the
resulting product was degreased at 400.degree. C., and fired at
2200.degree. C. in a normal-pressure argon atmosphere for 3 hours
to manufacture an integral honeycomb structured body, which was a
silicon carbide sintered body, and had a porosity of 42%, an
average pore diameter of 9 .mu.m, a size of 34.3 mm.times.34.3
mm.times.150 mm and the number of through holes 21 of 28
pcs/cm.sup.2 (large-capacity through holes: 14 pcs/cm.sup.2,
small-capacity through holes: 14 pcs/cm.sup.2).
[0185] Here, in the integral honeycomb structured body, only the
large-capacity through holes were sealed by plugs on the end face
on the outlet side, and only the small-capacity through holes were
sealed with the plugs on the end face on the inlet side.
[0186] (2) Next, an aggregated honeycomb structured body was
manufactured by using the resulting integral honeycomb structured
bodies.
[0187] By using a heat resistant sealing material paste containing
30% by weight of alumina fibers having a fiber length of 0.2 mm,
21% by weight of silicon carbide particles having an average
particle diameter of 0.6 .mu.m, 15% by weight of silica sol, 5.6%
by weight of carboxymethyl cellulose and 28.4% by weight of water,
a large number of the integral honeycomb structured bodies 20 were
combined together, and then cut by using a diamond cutter to form a
cylindrical ceramic block having a diameter of 144 mm and a length
of 150 mm.
[0188] In this case, the thickness of the sealing material layer 14
used for combining the integral honeycomb structured bodies 20 was
adjusted to 1.0 mm.
[0189] (3) Next, ceramic fibers made from alumina silicate (shot
content: 3%, fiber length: 0.1 to 100 mm) (23.3% by weight) as
inorganic fibers, silicon carbide powder having an average particle
diameter of 0.3 .mu.m (30.2% by weight) as inorganic particles,
silica sol (SiO.sub.2 content in the sol: 30% by weight) (7% by
weight) as an inorganic binder, carboxymethyl cellulose (0.5% by
weight) as an organic binder, and water (39% by weight) were mixed
and kneaded to prepare a sealing material paste.
[0190] Next, a sealing material paste layer having a thickness of
1.0 mm was formed on the peripheral face of the ceramic block by
using the above-mentioned sealing material paste. Further, this
sealing material paste layer was dried at 120.degree. C., so that
an aggregated honeycomb structured body functioning as a
cylindrical honeycomb filter for purifying (converting) exhaust
gases was manufactured.
[0191] (4) Next, .gamma.-alumina was mixed with water and a nitric
acid solution serving as a dispersant, and further ground by a ball
mill at 90 min.sup.-1 for 24 hours to prepare alumina slurry having
a particle diameter of 2 .mu.m, and the resulting slurry was then
poured into the integral honeycomb structured body and the
aggregated honeycomb structured body, and dried at 200.degree.
C.
[0192] The above-mentioned processes were repeated until the
alumina layer reached an amount of 60 g/L, and the resulting
structured body was fired at 600.degree. C.
[0193] Ce(NO.sub.3).sub.3 was put into ethylene glycol, and stirred
at 90.degree. C. for 5 hours to prepare an ethylene glycol solution
containing 6% by weight of Ce(NO.sub.3).sub.3. The integral
honeycomb structured body and the aggregated honeycomb structured
body on which the alumina layer was formed were immersed in this
ethylene glycol solution, and heated at 150.degree. C. for 2 hours,
and then heated at 650.degree. C. for 2 hours in a nitrogen
atmosphere, so that an alumina layer containing a rare-earth oxide
to be used for supporting a catalyst on the surface of the ceramic
fired body was formed.
[0194] Diamine dinitro platinum nitric acid ([Pt
(NH.sub.3).sub.2(NO.sub.2).sub.2]HNO.sub.3) having a platinum
concentration of 4.53% by weight was diluted with distilled water,
and the ceramic fired body on which the rare-earth oxide containing
alumina layer was formed was immersed, and this was heated at
110.degree. C. for 2 hours, and then heated at 500.degree. C. for 1
hour in a nitrogen atmosphere, so that 2 g/L of platinum catalyst
having an average particle diameter of 2 nm was supported on the
surface of the ceramic fired body. Thus, the manufacturing
processes for the integral honeycomb structured body and the
aggregated honeycomb structured body on which the catalyst was
supported were completed.
Examples 2 to 28
[0195] The same processes as Example 1 were carried out to
manufacture integral honeycomb structured bodies and aggregated
honeycomb structured bodies except that the cross-sectional shape
perpendicular to the longitudinal direction and the height and the
width of the protruded portion formed on the partition wall
separating adjacent large-capacity through holes from each other
were changed as shown in Table 1.
[0196] Here, the cross-sectional shape perpendicular to the
longitudinal direction of the integral honeycomb structured body
and the height of the protruded portion formed on the partition
wall separating adjacent large-capacity through holes from each
other were adjusted by changing the shape of a die for use in
extrusion-molding of the mixture composition.
Reference Examples 1 to 4
[0197] The same processes as Example 1 were carried out to
manufacture integral honeycomb structured bodies and aggregated
honeycomb structured bodies except that the cross-sectional shape
perpendicular to the longitudinal direction was changed into a
shape as shown in Table 1 and that a recessed portion having a
depth of 0.1 mm as shown in FIG. 1C was formed at the partition
wall separating large-capacity through holes from each other.
[0198] Here, the cross-sectional shape perpendicular to the
longitudinal direction of the integral honeycomb structured body
and the depth of the recessed portion formed at the partition wall
separating adjacent large-capacity through holes from each other
were adjusted by changing the shape of a die for use in
extrusion-molding of the mixture composition.
Reference Examples 5 to 8
[0199] The same processes as Example 1 were carried out to
manufacture integral honeycomb structured bodies and aggregated
honeycomb structured bodies except that the cross-sectional shape
perpendicular to the longitudinal direction, the height of a
protruded portion formed on the partition wall separating adjacent
large-capacity through holes from each other and the amount of the
alumina coat layer were changed as shown in Table 1.
[0200] Here, the cross-sectional shape perpendicular to the
longitudinal direction of the integral honeycomb structured body
and the height of a protruded portion formed on the partition wall
separating adjacent large-capacity through holes from each other
were adjusted by changing the shape of a die for use in
extrusion-molding of the mixture composition.
Comparative Examples 1 to 7
[0201] The same processes as Example 1 were carried out to
manufacture integral honeycomb structured bodies and aggregated
honeycomb structured bodies except that the cross-sectional shape
perpendicular to the longitudinal direction of the integral
honeycomb structured body was changed as shown in Table 1 in a
manner in which neither a protruded portion nor a recessed portion
was formed on the partition wall separating adjacent large-capacity
through holes from each other.
[0202] Here, the cross-sectional shape perpendicular to the
longitudinal direction of the integral honeycomb structured body
and the height of a protruded portion formed on the partition wall
separating adjacent large-capacity through holes from each other
were adjusted by changing the shape of a die for use in
extrusion-molding of the mixture composition.
(Evaluation 1; Pressure Loss)
[0203] As shown in FIG. 7, each of the aggregated honeycomb
structured bodies of the examples, reference examples and
comparative examples was placed in an exhaust passage of an engine
to form an exhaust gas purifying (converting) device, and the
engine was driven at the revolutions of 3000 min.sup.-1 and a
torque of 50 Nm so that the aggregated honeycomb structured body
was allowed to collect particulates of 8 g/L, and the pressure loss
of the resulting honeycomb structured body was then measured. Table
2 shows the results.
(Evaluation 2; CO-Light Off Temperature, HC-Light Off
Temperature)
[0204] Each of the integral honeycomb structured bodies of the
examples, reference examples and comparative examples was placed in
a reaction tester, and a simulation gas, which had component
concentrations of C.sub.3H.sub.6 (200 ppm), CO (300 ppm), NOx (160
ppm), SOx (8 ppm), CO.sub.2 (0.038%), H.sub.2O (10%) and O.sub.2
(13%), was introduced into the integral honeycomb structured body
at a space velocity (SV) of 45000/h so that, as the temperature of
the simulation gas was gradually raised, the gas concentrations
before and after the introduction of the gas into the honeycomb
structured body were analyzed. Then, the temperatures at which the
converting rates of CO and HC respectively reached 50% were defined
as CO-Light off temperature and HC-Light off temperature. Table 2
shows the results.
[0205] Here, with respect to the measuring device, a MEXA-7500D
(MOTOR EXHAUST GAS ANALYZER, manufactured by Horiba Ltd.) was used.
In this device, CO, CO.sub.2 and SO.sub.2 were detected by NDIR
(Non-Dispersive Infrared-absorbing system), O.sub.2 was detected by
MPOP (Magnetic Pressure System), HC was detected by FID (Hydrogen
Flame Ionization Detector), and NOx was detected by CLD.
(Evaluation 3; Filter Regenerating Test)
[0206] As shown in FIG. 7, each of the aggregated honeycomb
structured bodies of the examples, reference examples and
comparative examples was placed in an exhaust passage of an engine
to form an exhaust gas purifying (converting) device, and the
engine was driven so that the aggregated honeycomb structured body
was allowed to collect particulates of 7 g/L. Next, the aggregated
honeycomb structured body that had collected particulates was
placed in a reaction tester so that the temperature of the
aggregated honeycomb structured body was maintained at 200.degree.
C., with nitrogen gas being introduced into the aggregated
honeycomb structured body at a flow rate of 130 L/min.
[0207] Next, a simulation gas, which had approximately the same
composition as exhaust gases of a diesel engine except that no
particulates were contained therein, was introduced into the
aggregated honeycomb structured body under conditions of a
temperature of 650.degree. C., a pressure of 8 kPa and a flow time
of 7 minutes so that particulates were burned. In this case, a
honeycomb catalyst supporting body (diameter: 144 mm, length: 100
mm, cell density: 400 cells/inch, platinum: 5 g/L), made of
commercial cordierite, was placed at the simulation gas flow-in
side of the aggregated honeycomb structured body, and the
simulation gas that had passed through the honeycomb supporting
body was introduced into the aggregated honeycomb structured
body.
[0208] Lastly, the weight of the aggregated honeycomb structured
body was measured to find out a rate (filter regenerating rate) of
burned particulates to the collected particulates of 7 g/L so that
the purifying (converting) performance of particulates was
evaluated. Table 2 shows the results.
[0209] Here, the simulation gas had component concentrations of
C.sub.3H.sub.6 (6540 ppm), CO (5000 ppm), NOx (160 ppm), SOx (8
ppm), CO.sub.2 (0.038%), H.sub.2O (10%) and O.sub.2 (10%).
Moreover, the introduction of the simulation gas heated the
aggregated honeycomb structured body to about 600.degree. C.
TABLE-US-00001 TABLE 1 Cross-sectional Height of Width of Amount
shape of Aperture Ratio of protruded protruded of Al.sub.2O.sub.3
honeycomb ratio .alpha. aperture portion portion coat structured
body (%) ratios (mm) (mm) (g/L) Example 1 37.97 1.55 0.1 0.3 60
Example 2 0.3 0.3 60 Example 3 0.6 0.3 60 Example 4 44.79 2.54 0.1
0.3 60 Example 5 0.3 0.3 60 Example 6 0.6 0.3 60 Example 7 51.77
4.45 0.1 0.3 60 Example 8 0.3 0.3 60 Example 9 0.6 0.3 60 Example
10 59.04 6 0.1 0.3 60 Example 11 0.3 0.3 60 Example 12 0.6 0.3 60
Example 13 51.77 4.45 0.1 0.3 60 Example 14 0.3 0.3 60 Example 15
0.6 0.3 60 Example 16 51.77 4.45 0.1 0.3 60 Example 17 0.3 0.3 60
Example 18 0.6 0.3 60 Example 19 51.77 4.45 0.1 0.3 60 Example 20
0.3 0.3 60 Example 21 0.6 0.3 60 Example 22 51.77 4.45 0.1 0.3 60
Example 23 0.3 0.3 60 Example 24 0.6 0.3 60 Example 25 37.97 1.55
0.3 0.6 60 Example 26 44.79 2.54 0.3 0.6 60 Example 27 51.77 4.45
0.3 0.6 60 Example 28 59.04 6 0.3 0.6 60 Reference 37.97 1.55 0.1*
0.3 60 Example 1 Reference 44.79 2.54 0.1* 0.3 60 Example 2
Reference 51.77 4.45 0.1* 0.3 60 Example 3 Reference 59.04 6 0.1*
0.3 60 Example 4 Reference 37.97 1.55 0.3 0.3 30 Example 5
Reference 44.79 2.54 0.3 0.3 30 Example 6 Reference 51.77 4.45 0.3
0.3 30 Example 7 Reference 59.04 6 0.3 0.3 30 Example 8 Comparative
37.97 1.55 0 0 60 Example 1 Comparative 44.79 2.54 0 0 60 Example 2
Comparative 51.77 4.45 0 0 60 Example 3 Comparative 59.04 6 0 0 60
Example 4 Comparative 51.77 4.45 0 0 60 Example 5 Comparative 51.77
4.45 0 0 60 Example 6 Comparative 51.77 4.45 0 0 60 Example 7
Comparative 51.77 4.45 0 0 60 Example 8 Note) *Depth of recessed
portion (groove) (mm)
[0210] TABLE-US-00002 TABLE 2 Pressure CO-Light off HC-Light off
Filter loss temperature temperature regenerating (kPa) (.degree.
C.) (.degree. C.) rate (%) Example 1 9.8 149 188 77 Example 2 9.6
147 186 79 Example 3 9.4 143 184 84 Example 4 9.5 152 192 82
Example 5 9.4 149 190 85 Example 6 9.2 147 187 89 Example 7 9.7 156
197 74 Example 8 9.5 153 195 77 Example 9 9.3 150 192 83 Example 10
10.2 160 203 70 Example 11 10.1 156 200 72 Example 12 9.9 153 198
78 Example 13 10.3 159 197 69 Example 14 10.0 155 195 72 Example 15
9.8 152 193 76 Example 16 10.0 154 195 83 Example 17 9.8 151 192 86
Example 18 9.6 149 190 91 Example 19 10.1 155 197 73 Example 20 9.8
153 195 75 Example 21 9.7 150 192 79 Example 22 10.9 159 205 68
Example 23 10.6 157 201 71 Example 24 10.4 155 199 75 Example 25
9.8 151 190 82 Example 26 9.5 152 193 87 Example 27 9.7 155 199 82
Example 28 10.3 158 204 77 Reference 9.9 150 190 78 Example 1
Reference 9.7 154 193 83 Example 2 Reference 9.8 157 199 77 Example
3 Reference 10.2 161 205 72 Example 4 Reference 7.8 150 188 65
Example 5 Reference 7.5 151 193 71 Example 6 Reference 7.7 156 197
63 Example 7 Reference 8.1 157 202 60 Example 8 Comparative 11.3
150 190 58 Example 1 Comparative 11.1 153 193 55 Example 2
Comparative 11.4 157 200 52 Example 3 Comparative 11.8 162 205 54
Example 4 Comparative 11.7 157 200 50 Example 5 Comparative 13.0
153 198 55 Example 6 Comparative 11.5 156 199 51 Example 7
Comparative 13.3 159 203 49 Example 8
[0211] As shown in Table 1 and Table 2, in each of aggregated
honeycomb structured bodies according to the examples in which the
partition wall separating adjacently located large-capacity through
holes is provided with a protruded portion or a recessed portion
that serves as a selective catalyst supporting portion, a pressure
loss is lower even after a certain amount of particulates were
collected, and the regenerating rate of the filter is improved in
comparison with aggregated honeycomb structured bodies according to
comparative examples in which neither a protruded portion nor a
recessed portion is formed on the partition wall separating
adjacently located large-capacity through holes from each
other.
[0212] Moreover, in each of aggregated honeycomb structured bodies
according to the examples in which the partition wall separating
adjacent large-capacity through holes from each other is provided
with a protruded portion or a recessed portion that serves as a
selective catalyst supporting portion, both of the CO-Light off
temperature and HC-Light off temperature are slightly lowered in
comparison with aggregated honeycomb structured bodies according to
comparative examples in which neither a protruded portion nor a
recessed portion is formed on the portion of the partition wall
separating adjacent large-capacity through holes from each
other.
* * * * *